In-line packet processing

ABSTRACT

A method and apparatus for in-line processing a data packet while routing the packet through a router in a system transmitting data packets between a source and a destination over a network including the router. The method includes receiving the data packet and pre-processing layer header data for the data packet as the data packet is received and prior to transferring any portion of the data packet to packet memory. The data packet is thereafter stored in the packet memory. A routing through the router is determined including a next hop index describing the next connection in the network. The data packet is retrieved from the packet memory and a new layer header for the data packet is constructed from the next hop index while the data packet is being retrieved from memory. The new layer header is coupled to the data packet prior to transfer from the router.

BACKGROUND

The present invention relates generally to data routing systems, andmore particularly to methods and apparatus for efficiently routingpackets through a network.

In packet switched communication systems, a router is a switching devicethat receives packets containing data or control information on oneport, and based on destination information contained within the packet,routes the packet out another port to a destination (or an intermediarydestination). Conventional routers perform this switching function byevaluating header information contained within a first data block in thepacket. The header includes destination information that can be used indetermining the proper output port for a particular packet.

Efficient switching of packets through the router is of paramountconcern. Referring now to FIG. 1, a conventional router includes aplurality of input ports 2 each including an input buffer (memory) 4, aswitching device 6 and a plurality of output ports 8. Data packetsreceived at input port 2 are stored at least temporarily, in memory 4while destination information associated with each packet is decoded todetermine the appropriate switching through switching device 6.

Data packets include both header and data fields and can be of variablelengths. The header includes both format information related to the typeof packet and layer data. Networking protocols are defined in terms oflayers, with each layer responsible for different portions of thecommunications the network. For example TCP/IP is a standard Internetnetwork protocol that includes an application layer, transport layer, IPlayer (network layer or L3), link layer (L2) and physical layer (L1). Adata packet can include a plurality headers, one for each relevant layerthat is to handle the packet during routing. Each layer header caninclude source and destination information as well as other layerspecific information. To transfer the packet out of the switch, portionsof the header are required to be examined (e.g., Layer 2 and Layer 3, L2and L3 respectively, header information). Typically, packets are storedin memory 4 while header processing is performed.

Complicating the examination process, the format of the packet headerscan vary. Destination or other information (e.g., L3 information) maynot always be located at the same position in a header.

Unfortunately, conventional routers are inefficient in a number ofrespects. Conventional routers are incapable of processing packetsin-line. All of the packet header typically must be received prior tothe beginning of header processing. Packets are not screened early onfor faults necessitating additional bandwidth and resources for handlingthese bad packets.

SUMMARY OF THE INVENTION

In general, in one aspect, the invention provides a method of in-lineprocessing a data packet while routing the packet through a router in asystem transmitting data packets between a source and a destination overa network including the router. The method includes receiving the datapacket and pre-processing layer header data for the data packet as thedata packet is received and prior to transferring any portion of thedata packet to packet memory. The data packet is thereafter stored inthe packet memory. A routing through the router is determined includinga next hop index describing the next connection in the network. The datapacket is retrieved from the packet memory and a new layer header forthe data packet is constructed from the next hop index while the datapacket is being retrieved from memory. The new layer header is coupledto the data packet prior to transfer from the router.

Aspects of the invention include numerous features. The pre-processingstep includes screening header layer data associated with the datapacket for errors and dropping a bad data packet prior to transferringany portion of the data packet to packet memory. The screening includesscreening Layer 2 (L2) and Layer 3 (L3) headers for errors. The L2header can be examined to detect errors arising from unrecognized L2header formats and unconfigured L2 connections. The L3 header can beexamined to detect data packets with checksum errors, packet lengtherrors and L3 header errors.

The step of storing the data packet in memory includes dividing the datapacket into cells of a fixed size and storing the cells in a distributedmemory. The step of retrieving the data packet from memory includesreconstructing the packet from cells stored in the memory.

The pre-processing includes stripping L2 header data from a data packetprior to storage the packet memory, identifying the beginning of the L3header and examining the L3 header for errors prior to the storage ofthe data packet in, the packet memory. The next hop index is a pointerto a sequence stored in a storage device within the router and the stepof constructing a new layer header includes executing the sequence. Theexecution of the sequence includes retrieving a common template forconstructing a common portion of an L2 header to be attached to the datapacket and a custom template for constructing a unique portion of the L2header. The common and unique templates can be executable code operableto construct and associated portion of an L2 header for the data packet.

The step of receiving the data packet includes receiving a plurality ofdata packets for processing from a plurality of input ports representinga plurality of streams of data to be routed through the router. The stepof pre-processing the data packet includes dividing the data packet intofixed length cells and parsing the L2 header associated with the firstcell of the data packet prior to receipt of the entire data packet. Thestep of parsing the L2 header includes examining the L2 header forerrors and identifying the start of a next layer header in the datapacket.

The cells for a data packet can be temporarily stored in a queue afterL2 header parsing is completed. Consecutive cells in a data packet canbe sprayed to a different bank in the packet memory.

The method can include snooping while the cells are being written to thequeue and parsing the L3 header including examining the L3 header forerrors. A data packet can be dropped if errors are detected in the L2header during L2 header parsing without storing a cell associated withthe data packet in the queue.

In another aspect, the invention provides a router for in-lineprocessing a data packet while routing the packet in a systemtransmitting data packets between a source and a destination over anetwork including the router. The router includes a packet memory forstoring portions of the data packet, an input port for receiving a datapacket including a header processing engine for evaluating header layerinformation upon receipt and prior to the storage of the data packet inthe packet memory, a controller operable to determine packet routingthrough the router and output a next hop index indicating the nextconnection in the network for each data packet to be routed through therouter and an output port for transferring the data packet to thedestination. The output port includes a output formatter forconstructing a layer header for the data packet to facilitate thetransfer of the packet to the destination.

Aspects of the invention include numerous features. The headerprocessing engine is operable to screen header layer data associatedwith the data packet for errors and drop a bad data packet prior totransferring any portion of the data packet to packet memory. The headerprocessing engine screens Layer 2 (L2) and Layer 3 (L3) headers forerrors. The header processing engine examines the L2 header to detecterrors arising from unrecognized L2 header formats and unconfigured L2connections. The header processing engine examine the L3 header todetect data packets with checksum errors, packet length errors and L3header errors.

The router can include a cell packetizer operable to divide the datapacket into cells of a fixed size prior to transfer to packet memory.The packet memory can be a distributed memory and the router can includea spray engine for distributing cells across the distributed memory.

The header processing engine strips L2 header data from a data packetprior to storage the packet memory, identifies the beginning of an L3header and examines the L3 header for errors prior to the storage of thedata packet in the packet memory. The next hop index is a pointer to asequence stored in a storage device within the router and the outputformatter executes the sequence to construct a new layer header. Thestorage device includes a common template for constructing a commonportion of an L2 header to be attached to the data packet and a customtemplate for constructing a unique portion of the L2 header. The storagedevice is distributed and includes a local portion within the outputport and a remote portion elsewhere in the routing device and where thecommon template is stored in local portion and the custom template isstored in the remote portion. The common and unique templates areexecutable code operable to construct and associated portion of an L2header for the data packet. The router can further include a pluralityof input ports and a plurality of output ports, each of the input portsand output ports configurable to receive and process a plurality of datapackets representing a plurality of streams of data to be routed throughthe router.

The router can further include a cell packetizer operable to divide thedata packet into fixed length cells and a L2 parsing engine operable toexamine the L2 header associated with the first cell of the data packetprior to receipt of the entire data packet. The L2 parsing engine isoperable to examine the L2 header for errors and identify the start of anext layer header in the data packet.

The router can further include a queue operable for temporarily storingthe cells for a data packet after L2 header parsing is completed and aspray engine operable to spray consecutive cells in a data packet to adifferent bank in the packet memory.

The router can further include a L3 parsing engine operable to snoopwhile the cells are being written to the queue and parse the L3 headerincluding examining the L3 header for errors. The L2 parser engine isoperable to drop a data packet if errors are detected in the L2 headerduring L2 header parsing without storing a cell associated with the datapacket in the queue.

In another aspect the invention provides a method of routing a datapacket through a router in a system transmitting data packets between asource and a destination over a network including the router. The methodincludes receiving the data packet and dividing the data packet intocells of a fixed size. While dividing the data packet, layer header datafor the packet is pre-processed to locate the beginning of a next layerheader. The cells are stored in a distributed memory. Prior to storing afirst cell in the distributed memory associated with the packet, headerlayer data is screened for errors and a bad packet is dropped prior totransferring any cells into the distributed memory. A routing throughthe router is determined including a next hop index describing the nextconnection in the network. The packet is reconstructed from cells storedin the memory and new layer header data for the packet is constructedfrom the next hop index.

Among the advantages of the invention are one or more of the following.Packets are processed in-line and input buffering is minimized by theuse of shared buffers. Packet pre-processing is accelerated by usingmultiple embedded micro-code engines to perform L2 header processing forreceived packets. Pre-processing includes segmentation of the packetsinto cells and distribution of the cells across memory within the routerwhile processing L3 header data in parallel. Packet header screening isaccomplished early on prior to the receipt of all of the data associatedwith the header of a given packet. Early packet screening reducesbandwidth and frees resources in the router.

Other advantages and features will be apparent from the followingdescription and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional router device.

FIG. 2 a is a schematic block diagram of a data routing system accordingto one embodiment of the present invention.

FIG. 2 b is a schematic block diagram of a router according to oneembodiment of the present invention.

FIG. 3 a is a schematic block diagram of an multi-function portaccording to one embodiment of the present invention.

FIG. 3 b is a schematic block diagram showing data transfers betweencomponents of the router of FIG. 2 b according to one embodiment of thepresent invention.

FIG. 3 c is a schematic block diagram of the input section of amulti-function multiport according to one embodiment of the invention.

FIG. 3 d is a schematic block diagram of the data handler of amulti-function multipart according to one embodiment of the invention.

FIG. 3 e is a data structure for a cell transferred between amulti-function port and an input switch according to one embodiment ofthe present invention.

FIG. 4 is a schematic block diagram of a router showing the timing andordering of transfers from a multi-function multiport to the inputswitch according to one embodiment of the present invention.

FIG. 5 is a data structure for an output request transferred from thecontroller to the output switch according to one embodiment of thepresent invention.

FIG. 6 is a schematic block diagram for an output section of amulti-function port according to one embodiment of the presentinvention.

FIG. 7 is a flow diagram for a process of routing a packet through arouter according to one embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 2 a, in a packet switching system, a source 10 isconnected to one or more routers 20 for transmitting packets to one ormore destinations 30. Each router includes a plurality of multi-functionmultiports that are connected to various sources and destinations. Apacket from source 10 can pass through more than one router 20 prior toarriving at its destination.

Referring to FIG. 2 b, each router 20 includes an input switch 100, anoutput switch 102, a global data buffer 104 including one or more memorybanks 105, a controller 106 and a plurality of multi-function multiports150 (150-0 through 150-3, respectively). Associated with the controller106 is controller memory 109 for storing a routing table. Input switch100 and output switch 102 are connected to each multi-function multipart150 in router 20. In one embodiment, router 20 includes plug-and-playmulti-function multiports which allows for easy expansion capability.The present invention will be described with reference to a systemincluding eight multi-function multiports 150 (even though FIG. 2 b onlyshows four), with each multi-function multiport including up to sixteeninput ports and sixteen output ports. Other configurations can be useddepending on user load conditions. Each multi-function multipartincludes one or more input ports, one or more output ports and a memory.The configuration and operation of the multi-function multiports will bedescribed in greater detail below.

In operation, packets are received at a multi-function multiport 150,transferred to input switch 100 and stored temporarily in global databuffer 104. When the packet is received by input switch 100, a key isread from the packet and transferred to controller 106. The key containsdestination information which is derived from a header field associatedwith the first block of data in a packet and other information (such assource ID, priority data and flow ID).

A route look-up engine 110 in controller 106 performs a tree basedsearch based on the key information and returns a result that includesthe output multipart associated with the destination. The result iscoupled with other information (such as source ID, flow ID and packetlength) for routing the packet through router 20 and provided as anotification from controller 106 to output switch 102. Output switch 102transfers the notification to the identified multi-function multipart150. Upon receiving the notification information, the multi-functionmultiport 150 initiates the transfer of the packet from global databuffer 104 through output switch 102 to the appropriate multi-functionmultipart 150.

Multi-function Multiports

Referring to FIG. 3 a, each multi-function multiport 150 includes aninput section 270, an output section 280 and a memory section 290.

Input section 270 includes a line input interface 300, a data handler302 and an input switch interface 304.

Output section 280 includes an output request processor 306, a lineoutput interface 308, a storage device 310, stream output buffers 312(one for each output stream), output formatter 314, an output switchinterface 316 and head and tail queue buffer 318. In addition, theoutput section includes a portion of input switch interface 304.Specifically, input switch interface 304 includes read request queues305, one for each memory bank. The use and operation of the read requestqueues, stream output buffers, and head and tail queue will be discussedin greater detail below in association with FIG. 6.

Memory section 290 includes a memory bank 105 (which represents aportion of the global data buffer 104) and a notification queue body319.

The multi-function multiport is used in conjunction with the inputswitch, output switch and controller as is shown in FIG. 3 b. Thevarious piece components of the input section, output section and memorysection will be described in greater detail below. The combination ofthe input, output and memory sections into a single unit simplifies theinterfaces between the components.

Referring again to FIG. 3 a, packets are received at line inputinterface 300. As the packets are received, data handler 302 divides thepackets received into fixed lengths cells. In one embodiment, the lengthof each cell is 80 bytes, with 16 bytes of internal header (controlinformation) and 64 bytes of cell data. As the data handler divides theincoming packets into fixed length cells, it synchronously outputs thecells to input switch 100 through input switch interface 304.

As described above, packets are divided into data cells and transferredinto the global data buffer 104 for temporary storage during the look-upprocess. Data handler 302 of input section 270 divides the packets intodata cells and examines data format information (L2/L3 information) fromeach packet prior to storage of the packet in the global data bufferportion of memory 104 (FIG. 2 b). In one implementation shown in FIG. 3c, data handler 302 includes a packing queue 380, L2 pattern matchdecoder 382, L3 decoder 384, cell segmentation engine 386, cell payloadqueue 388, cell header queue 390 and bank spray engine 392.

Each multifunction multipart includes a line input interface 300 thatcan include up to 16 input ports for receiving data from up to 16 activestreams. Each multi-function multipart is configurable to accommodatestreams of various formats and in one implementation supports a 2.4 Gbps(OC-48) full duplex interface. Other input configurations are availablewith an accumulated bandwidth of up to 2.4 Gbps, including up to 16streams of OC-3 bandwidth. Other configurations include 12 streams ofOC-3 bandwidth and one stream of OC-12 bandwidth. Packing queue 380receives the various input stream data on the input ports and packs thestream data into data words for transfer to segmentation buffer 387 (upto 64 bytes in one implementation). Packing queue 380 includes perstream queues for accumulating data from each stream.

Referring to FIG. 3 d, the packing process is performed in two phases.In a first phase, 8 bit or 32 bit data is accumulated in a bit packingqueue 381 a. Bit packing queue 381 a includes stream bit packing queues(381 a-1 thru 381 a-16), one for each stream. In one implementation, bitpacking queue 381 a includes 16 stream bit packing queues (whensupporting 16 OC-3 streams). Bit packing queue 381 a includes acontroller 385 a for streaming data words from the bit packing queue toa byte packing queue 381 b. Each stream bit packing queue can be sizedto hold two or more words of data, and in one implementation are sizedto hold three 64 bit words of data (8 byte data words). Associated witheach data word stored in the stream bit packing queues are control flagswhich are received along with the stream data. In one embodiment, five(5) bits of flag data are stored with each 64 bit data word in eachstream bit packing queue. The five flag data bits are passed with each64 bit word from the bit packing queue 381 a to the byte packing queue381 b.

In one embodiment the control flags include an end of packet withouterror flag (1 bit), a end of packet with error flag (1 bit), and a lastbyte pointer (3 bits). The size of the last byte pointer indicates thelast byte in the eight (8) byte word of data that contains data in thetransfers between the bit packing queue 381 a and byte packing queue 381b. In one implementation, line input interface 300 screens the incomingpackets and generates the control flag data. The control flag data canbe advantageously used in screening packets prior to transfer to theglobal memory. More specifically, errors detected by the line inputinterface 300 are reconciled during L2 header processing. A packet thatis written to segmentation buffer 387 that has an error flag set isnever transferred by the packetizer 391 to payload buffer 388. Dataassociated with the packet is overwritten in time by a next 64 byte dataword from byte packing queue 381 b. Other early error detection methodsare described in greater detail below in association with L2 and L3processing.

Based on the availability of data in the individual stream bit packingqueues, a single 64 bit word is transferred per clock cycle bycontroller 385 a from bit packing queue 381 a to byte packing queue 381b. Controller 385 a cycles through the individual bit packing queues ina round-robin fashion to transfer available data words to byte packingqueue 381 b.

In a second phase of the packing process, byte packing queue 381 baccumulates eight (8) byte portions of data (64 bit data words) prior tosegmentation. Byte packing queue 381 b includes stream byte packingqueues (381 b-0 thru 381 b-15), one for each stream. In oneimplementation, byte packing queue 381 b includes 16 stream byte packingqueues to support 16 streams of OC-3 data. Depending on the format ofthe stream data received, a lesser number of the stream byte packingqueues can be used. Byte packing queue 381 b is sized to, support theinput bandwidth, which in one implementation is 2.4 Gbps. Byte, packingqueue 381 b is configurable to support a variety of input streamconfigurations. Byte packing queue 381 b can be a flexible buffer whoseresources are dynamically allocated at start-up depending on the inputconfiguration.

Byte packing queue 381 b includes a cell dispatcher 385 b for streamingdata words from byte packing queue 381 b to segmentation buffer 387.Each stream byte packing queue can be sized to hold N or more words ofdata, and in one implementation each is sized to hold eighteen (18)eight (8) byte data portions (64 bit data words). Associated with eachdata word stored in the stream byte packing queues are control flagswhich are received along with the stream data.

Depending on the input configuration of the stream data received, alesser number of divisions for byte packing queue 381 b may be required.For example, when supporting four OC-12 streams, byte packing queue 381b is configured with four byte packing queues to accumulate 64 bit datawords for transfer to segmentation buffer 387.

Cell dispatcher 385 b operates in a round-robin fashion to cycle throughthe various individual stream byte packing queues to extract data wordsfor transfer to segmentation buffer 387. In one embodiment, eight (8)byte read cycles are used to transfer data from the individual bytepacking queues to segmentation buffer 387.

Each byte packing queue signals to the cell dispatcher when anappropriate number of data words have been accumulated and thus therespective byte packing queue is ready for servicing. A stream bytepacking queue initiates a signal to cell dispatcher 385 b indicatingdata is ripe for transfer upon the occurrence of one of three triggerconditions: upon receipt of the first 96 bytes of a new packet; uponreceipt of an end of packet flag; or upon receipt of 64 bytes of datawhich do not comprise the beginning or the end of a packet. The flagsreceived along with the data words from the bit packing queue 381 a areused to evaluate the data words received from byte packing queue 381 ato determine when the various conditions have been satisfied.

The individual stream byte packing queues are sized to ensure thatentries received from bit packing queue 381 a are not lost while waitingfor service by cell dispatcher 385 b. In an embodiment that includes 16OC-3 input streams, all of the stream byte packing queues areidentically sized to include eighteen 64 bit words.

L2 Header Processing

As described above, data words are transferred from byte packing queue381 b to segmentation buffer 387 as they become available. In addition,coincident with the transfer, the first 32 bytes of data packet (four 8byte data words) are also transferred to L2 header buffer 383 of L2pattern match decoder 382. For middle packets which include up to 64bytes of data in the middle of a packet, cell dispatcher 385 b disablesthe transfer of data to the L2 header buffer and no L2 header processingis required. The present invention processes packets in-line. In-lineprocessing includes two components, one at the input prior to storage ofa packet (or portion of the packet in packet memory, i.e. memory 104 ofFIG. 2 b) and the other at the output after packets are read from packetmemory. The input component conditionally strips the L2 header, findsthe start of the L3 header and checks the L3 header for errors. Inaddition, other early error verifications can be performed to assurethat bad packets are dropped prior to storage in packet memory. Theoutput component attaches a new L2 header to a packet and updatescertain L3 header fields as required. In-line processing significantlyincreases throughput in the router allowing for the early dumping ofpackets prior to storage in packet memory. The input component isdescribed immediately below. The output component is described later inthe specification.

While the first 32 bytes of a packet are transferred to L2 header buffer383, a flag is set and passed to L2 header parser 389 indicating apacket is available to process. Associated with L2 header parser 389 isa decoder 409 for processing L2 header information for each packet.Decoder 409 can include a micro-coded engine or subroutine operating todecode header information (L2 header information). In the implementationshown, the micro-coded engine includes four sub-processes 409-0 through409-3. The number of sub-processes can be selected to minimize thenumber of clock cycles required to examine the L2 header information. L2header parser 389 under the control of decoder 409 consumes bytes storedin L2 header buffer 383 to locate a header offset. The header offsetindicates the end of the L2 header and the beginning of the next layer,header (e.g., L3 header) for a given packet.

In addition, the L2 header parser examines portions of the L2 header forerrors. Errors arising form unrecognized L2 headers, unconfigured L2connections, or other L2 errors are immediately identified and droppedprior to being written to memory. In one implementation packets aredropped by never transferring the packet out of the segmentation buffer387. The dropped packet is overwritten in time by a next 64 byte dataword from byte packing queue 381 b.

Associated with the L2 header parser is a per stream L2 state queue 419.Per stream state queue 499 stores flags associated with a micro-codestarting address, priority (precedence) flag for the stream, aninterface index mapping to one or more logical interfaces, virtualconnection stream state information and channel stream stateinformation. The per stream state queue stores information associatedwith each stream so as to assure continuity in steam processing.

Segmentation buffer 387 is sized to accommodate up to eight data word(64 bytes) in one implementation. Associated with the segmentationbuffer is a selectable start read pointer that indicates the location inthe segmentation buffer to begin read operations (when reading data fromthe segmentation engine by packetizer 391). Data bytes are read frombyte packing queue 381 b and stored in segmentation buffer 387.Subsequent byte transfers (beyond the first 64 bytes) from byte packingqueue 381 b can result in a wrap around condition. Wrap around resultsin the overwriting of a portion of the contents of the segmentationbuffer. Wrap around may arise when a portion of the L2 header isoverwritten in accordance with the strip offset determined as part of L2header processing. A circular buffer can be used to minimize the size ofthe buffer required to support the line rate processing.

The segmentation buffer provides temporary storage of the data wordstransferred from the byte packing queue while the L2 processingcompletes. Transfer from segmentation buffer 387 by cell packetizer 391to cell payload queue 388 is initiated upon completion of the L2processing and delivery of the offset information to cell packetizer391. Cell dispatcher 385 b triggers the transfer of middle data words ina packet (all data words after the first data word associated with apacket).

In one implementation, segmentation buffer 387 can be a dual outputported device that includes two output ports for providing data bytes tocell packetizer 391 at twice the input rate. The dual porting allows forthe reading of up to sixteen bytes of data from segmentation buffer 387during a single read cycle by cell packetizer 391.

Cell Formation

Cell packetizer 391 is an engine that services cell segmentation buffer387 providing a cell sized amount of data to cell payload queue 388. Asdescribed above, cells are the preferred storage mechanism for storing afixed portion of a packet. Each cell includes a data portion and aheader portion. In one implementation, cell packetizer 391 transfers 64bytes of data to cell payload queue 388. Cell packetizer receives as aninput cell data from segmentation buffer 387 and from the segmentationstate queue 401 as well as offset information from L2 pattern matchdecoder 382. The operation of the segmentation state queue 401 isdescribed in detail below.

As described above, the offset information is derived from the L2 packetheader. The offset information can be provided in the form of a pointerpointing to a particular location in the data stored in segmentationbuffer 387. The pointer can be used to indicate the particular byte inthe data transferred from the segmentation buffer that marks thebeginning the next layer header. Cell packetizer 391 can discard thoseportions of the data that belong to the L2 header necessitating furtherreads from the byte packing queue 381 b to fill a data portion of a cell(64 byte) in cell payload queue 388.

The offset may not arise exactly on an eight byte boundary necessitatingthe storage of overflow data. To facilitate block transfers from bytepacking queue 381 b to segmentation buffer 387 (8 byte blocks), anoverflow queue is provided. Segmentation state queue 401 includes aqueue sized to contain N−1 bytes of data for each stream, where N isequal to the size of the block transfers from byte packing queue 381 bto segmentation buffer 387. Extra bytes that are required to be readfrom byte packing queue 381 b to facilitate the filling of a cell incell payload queue 388 are stored in segmentation state queue 401.

At the beginning of a cell packing operation, cell packetizer 391 firstchecks to determine if extra bytes for the stream being processed arepresent in segmentation state queue 401. If so, the extra bytes areloaded first prior to the loading of bytes from the segmentation buffer387. A cell segmentation engine 400 oversees the transfer of data fromsegmentation state queue 401 to cell packetizer 391. In oneimplementation, each queue in the segmentation state queue 401 stores upto seven leftover bytes of data that may have been required to be readin order to fill the previous cell associated with the given stream.

The position in cell payload queue 388 to which the cell is written iscontrolled by buffer pool manager 393. Cell dispatcher 385 b receivesfeedback from buffer pool manager 393 as entries are extracted from cellpayload queue 388. A slot must be available in cell payload queue 388prior to the packetizing of the cell data and extraction from bytepacking queue 381 b. Buffer pool manager includes a pointer thatindicates the next available cell in the cell payload queue that can bewritten to by cell packetizer 391. As each cell is written into cellpayload queue 388 an associated header is written into the cell headerqueue 390.

Ordering of cells at the stream level is accomplished through use ofcell state queue 402. Cells in the same stream must be extracted fromcell payload queue 388 in sequential order. Ordering is achieved bywriting a code to a per stream queue 388 as each cell is transferredinto cell payload queue 388. More specifically, for each write of a dataportion of a cell by cell packetizer 391 into cell payload queue 388,cell segmentation engine 400 writes a code that is stored in cell statequeue 402. Cell state queue 402 includes a queue for each stream in theinput. As each cell is written to cell payload queue 388, a codeincluding address and state information is written to cell state queue402. The address information includes a pointer to the location of thedata portion of the cell in cell payload queue 388. The stateinformation includes information indicating whether the cell is thefirst cell, middle cell or last cell in a packet. In one implementation,the code is 10 bits in length and includes two (2) bits indicatingwhether the cell is a first cell, middle cell or last cell as well aseight (8) bits of address information.

L3 Header Processing

The next layer header processing can be performed in parallel to thedata transfers to the cell payload queue. In one implementation, L3header processing is performed in parallel to the packing of data bycell packetizer 391. L3 header parser 406 snoops on the bus between thecell packetizer and cell payload queue 388 examining the L3 header datato derive a header to be stored in an associated entry in cell headerqueue 390.

Associated with L3 header parser 406 is a L3 state buffer 408. The L3state buffer 408 includes a plurality of queues, one for each stream,and operates to store L3 header information derived from a previousportion of a packet by L3 header parser 406. L3 header data can extendbeyond the first 64 bytes of a data packet. Accordingly, L3 headerprocessing can begin and then be delayed due to insufficient data (notall of the L3 header information is part of the first 64 byte data wordassociated with a packet). Alternatively, L3 processing can be delayeduntil receipt of all of the L3 header data. In either case, L3 statebuffer 408 is used to store L3 state information while waiting for asecond data portion for a packet in the same stream to be processed bycell packetizer 391.

L3 header processing includes error checking for checksum errors, packetlength errors, or other L3 header errors. If an error is detected, thenthe pointer associated with a cell that is written to the cell payloadqueue 388 is not committed. Pointers associated with cells in the cellpayload queue are stored in cell state queue 402. The operation of cellstate queue 402 is described in greater detail below.

Cell headers are constructed and stored in cell header queue 390. Theformat for a cell header is described in greater detail below inassociation with FIG. 3 e. L3 header parser 406 examines L3 header datawhile snooping on the bus to derive values for the various L3 flagsstored in a cell header. L2 header parser 389 derives a series of L2flags while processing the L2 header. These flags are used by thelook-up engine and are based on the type of L2 packet received. L2/L3header merge 407 collects L2 flag data from L2 header parser 389 andstores the flag data temporarily while the L3 header is processed. L3flags detected by the L3 header parser are combined with the L2 flagsand stored in the cell header.

The flags store information required for the efficient down-streamprocessing of a given packet. In one implementation, the L2 flagsderived during L2 processing include a packet loss priority flag, a sendpacket to processor flag, a sample packet flag and a physical multicastflag. The L3 flags derived during L3 header processing include an optionflag, packet priority flag, transmission control protocol (TCP) flag,protocol type flag, and DF (don't fragment) flag.

The packet loss priority flag is used to determine a priority forpackets that are dropped due to congestion in an output port of therouter. The dropping of packets due to congestion is described ingreater detail in co-pending patent application entitled “HIGH SPEEDSWITCHING DEVICE”, filed Apr. 18, 1997, assigned Ser. No. 08/844,171,which is hereby expressly incorporated by reference.

The send packet to processor flag indicates that a packet is not to beforwarded out from the router and only sent to the controller forprocessing. The sample packet flag indicates that a packet is to beforwarded (to the appropriate output port) and also sent to thecontroller for processing. The physical multicast flag identifiesmulticast packets.

The option flag indicates that the packet has an option header(indicates that the L3 header is greater than the minimal size, e.g., 20bytes for IPV4 packets). The packet priority flag indicates the priorityof the packet and is used by the output portion of the multi-functionmultipart. The TCP flag indicates the packet is a TCP packet. Theprotocol flag indicates the L3 protocol type. The protocol flag is usedby the input switch to determine the length of the key to be passed tothe controller. The DF flag indicates whether the packet is to befragmented. Fragmentation may occur at the output interface depending onthe configuration of the particular interface. Setting the DF flag willresult in the dropping of the packet at the output interface rather thanfragment.

The header of a cell is generated from data associated with the celltype (indirect cell, direct cell, and data cells) along with headerflags extracted during L2 and L3 header processing as described above.In one implementation, the position in the cell header queue 389 thatthe header is written to is derived from the location in the cellpayload queue 388. The parallelism of the addressing for headers andcell data portions simplifies cell processing.

Spraying of Packets Across Memory Banks

Bank spray engine 392 includes a spray bank queue 395, cell spray engine396 and bank queue engine 397. The queues in cell state queue 402 areserviced by cell spray engine 396. Spray engine 396 sequences throughthe queues and delivers addresses associated with cells to spray bankqueue 395. Spray bank queue 395 includes a plurality of queues, one foreach active memory bank in the router one implementation, spray bankqueue 395 includes eight queues corresponding to eight memory banks.Entries in the cell state queues are serviced sequentially and providedas an input to a queue in spray bank queue 395. Consecutive entries in aqueue associated with a particular stream in cell state queue 402 aresprayed sequentially to the queues of spray bank queue 395.

Spray bank queue 395 is serviced in a strict round-robin fashion by bankqueue engine 397. Bank queue engine 397 receives as an input the nextentry from spray bank queue 395. Each entry indicates both an address inthe cell payload queue 388 for the next cell to be processed as well asan indication of whether or not the cell is a first cell, middle cell orlast cell to be processed. Bank engine queue 397 extracts the indicatedcell data from payload queue 388 and the associated header informationfrom cell header queue 390. The complete cell is provided as an outputto input switch interface 304.

The format for transfers between the multi-function multipart and theinput switch is shown in FIG. 3 e. A cell 350 transferred from amulti-function multipart 150 to the input switch contains a cell header352 and cell data 354. Cell header 352 includes a type field 356, streamfield 358, and packet header fields 360. In addition, cell header 352includes an independent read request in the form of a multi-functionmultipart identifier 366 and address 368.

The type field 356 indicates the type of cell to be transferred from themulti-function multipart. At each cell slot (20 clock cycles in oneembodiment), a multi-function multipart can transfer either a data cell,an indirect cell placeholder, or a delayed indirect cell placeholder.Data cells contain data associated with an incoming packet. An indirectcell placeholder is an empty cell, and is used in conjunction withindirect addressing for the storage of the cells in the global databuffer 104. Delayed indirect cell placeholders arise when a data streamthat requires indirect addressing terminates at a time prior to thedesignated time for writing the last indirect addressing cell associatedwith the data stream to global data buffer 104. The generation andoperation of indirect placeholders and delayed indirect placeholderswill be discussed in greater detail below in conjunction with FIG. 7.

Stream field 358 indicates the stream to which the cell data belongs. Inone embodiment of the present invention, each multi-function multipartis capable of handling up to sixteen separate streams of data at a time,one on each of its respective 16 input ports.

Packet header field 360 contains header information associated with agiven packet and includes start offset information, packet length,interface index information and L2 and L3 flags generated as part of theL2 and L3 decoding processes recited above.

Multi-function multiport identifier 366 identifies the multi-functionmultiport which is sourcing the read request. Address 368 indicates theaddress in global data buffer 104 to be read.

Referring now to FIG. 4, a single cell 450 is transferred from amulti-function multiport 150 to input switch 100 at each cell (time)slot “T”. For a given cell slot “T”, input switch 100 receives a totalof “N” cells, where “N” is equal to the number of multi-functionmultiports.

In one embodiment, cells from a given stream can be written to memory inan order that is different from the arrival order. These out of orderwrites are performed to make efficient use of scarce bandwidth betweenthe multi-function multiports and the input switch. When a packet comesin to the multi-function multiport, it is broken up into cells asdescribed above as the bytes arrive and the cells are placed in per-bankoutput queues on the way to the input switch. These queues are designedto share scarce interconnect bandwidth between the streams of amulti-functional multiport in the most efficient way possible, but theyhave the detrimental effect of reordering cells at the interface betweenthe multi-function multiport and the input switch. Thus the cells from agiven stream can arrive at the input switch out of order. Themulti-function multiport marks the data cells of a stream with one offour codes: first cell (FC); intermediate data cell (DC); last cell(LC); or first cell which happens to be also a last cell (FLC).

Input Switch

Referring again to FIG. 2 b, input switch 100 routes cells to globaldata buffer 104. The architecture of input switch 100 and the routing ofcells through the input switch 100 is described in greater detail inco-pending patent application entitled “HIGH SPEED SWITCHING DEVICE”,filed Apr. 18, 1997, assigned Ser. No. 08/844,171.

Memory Architecture

The memory architecture and routing of cells through global data buffer104 is described in greater detail in co-pending patent applicationentitled “HIGH SPEED SWITCHING DEVICE”, filed Apr. 18, 1997, assignedSer. No. 08/844,171.

Incoming packets are broken up into as many cells as needed and thecells are written to the global data buffer as they arrive. The globaldata buffer is treated as a single large circular buffer. The inputswitch maintains an array of write pointers, one per active bank, tokeep track of where to write the next cell. The pointers start out atone end of the buffer and advance until they eventually wrap around andoverwrite packets that were written a long time ago. An ageing mechanismis used to guard against reading cells that may have been overwritten bysubsequent packets. The cells of packets arriving on a given stream areinterleaved strictly across the active banks to spread the bandwidthload.

Controller

Controller 106 includes controller memory 109, route look-up engine 110,an input switch interface and output switch interface. Controller 106receives a route look-up request from input switch 100 at the inputswitch interface. Controller 106 performs a best match look-up andoutputs a notification through the output switch interface to outputswitch 102. The process of matching keys retrieved from a packet inorder to determine a best match route through the router is described ingreater detail in co-pending patent application entitled “HIGH SPEEDVARIABLE LENGTH BEST MATCH LOOK-UP IN A SWITCHING DEVICE”, filed on Dec.16, 1996, by Fergusen et al., Ser. No. 08/767,576, which is herebyexpressly incorporated by reference.

The notification includes a result which indicates the multi-functionmultiport to be used in the transfer of the packet to its destination.

Referring now to FIG. 5, the data structure associated with thenotification outputted by the controller 106 to the output switch 102 isshown. Th data structure 1400 for the notification includes a mask 1402,a next hop index pointer 1404, full address 1406, offsets 1408 andpacket length 1410.

The mask field 1402 is used to indicate which multi-function multiportconnected to output switch 102 is to transfer the packet. In oneembodiment, the notification can be sent to more than one multi-functionmultiport resulting in the broadcast of the associated packet.

Associated with each multi-function multiport 150 is a storage 310. Thenext hop index pointer points to a location in storage 310. Storage 310is used to store media header information associated with a particulartype of packet transfer. Next hop addresses, media headers and storage310 will be described in greater detail below in association with theoutput section of multi-function multiport 150.

The full address 1406 indicates the starting address in the global databuffer where the first cell in the packet is stored. As was describedabove, offsets 1408 provide linking information for retrieving cells oran indirect cell associated with the packet. Packet length filed 1410indicates the length of the associated packet and can be used todetermine if indirect cells will have to be retrieved.

Output Switch

Referring again to FIG. 2 b, output switch 102 processes notificationsreceived from controller 106 for transfer to an appropriatemulti-function multiport 150. The architecture and routing of cellsthrough output switch 102 is described in greater detail in co-pendingpatent application entitled “HIGH SPEED SWITCHING DEVICE”, filed Apr.18, 1997, assigned Ser. No. 08/844,171, which is hereby expresslyincorporated by reference.

Output Section of a Multi-Function Multiport

Referring now to FIG. 6, each multi-function multiport 150 includes anoutput switch interface 316, an input switch interface 304 includingread request queues, head and tail queue buffer 318, an output requestprocessor 306, an line output interface 308, storage device (memory)310; stream output buffers 312 and output formatter 314.

A multi-function multiport 150 receives notification that a packet is tobe processed in the form of a notification received at the output switchinterface 316. Output request processor 306 processes notifications,storing each in an appropriate location in head and tail queue buffer318 and servicing notification requests as they make their way throughthe various-priority queues in head and tail queue buffer 318. Theservicing of requests results in the generation of a read request toinput switch 100 associated with the first address in memory where thepacket (associated with the particular notification) is stored in theglobal data buffer. The architecture and operation of the notificationqueues is described in greater detail in co-pending patent applicationentitled “HIGH SPEED SWITCHING DEVICE”, filed Apr. 18, 1997, assignedSer. No. 08/844,171.

As cells are received back at the multi-function multiport 150(responsive to the read requests), they are stored in an associatedstream output buffer 312. Stream output buffer 312 includes a pluralityof FIFOs, one for each stream. Each cell received for a stream is placedin the streams associated FIFO. For given packet, the multi-functionmultiport stores a fixed number of cells (in the FIFO) required toprovide a streamed output prior to initializing the output of the streamto line output interface 308. In one embodiment of the presentinvention, twelve cells are stored prior to beginning output (streamdata) from the output port. The selection of the number of cells forstorage in output buffer 312 is based on the latency in the read process(number of clock cycles between a read request from an multi-functionmultiport and the arrival of the cell associated with the read requestto the output port).

Output formatter 314 receives the cells from output buffer 312 andcouples the data with media header information stored in memory 310.Each request (notification) received from output switch 102 includes anext hop index. The next hop index indicates the starting address inmemory 310 of the media header information associated with a given typeof transmission (derived from the destination of the packet). Mediaheader information stored in memory 310 can be loaded in memory 310 uponinitialization of the router and updated by the controller as required.The media header information includes all pertinent L2 constructionparameters as well as L3 protocol type information for L2/L1 in-lineheader re-writing operations.

As described above, “tin-line” packet processing includes an outputcomponent that constructs a new L2 header for a given packet prior totransfer out of the router. Output formatter 314 constructs a new L2header based on the media header information. In one implementation, thenext hop index points to a sequence capable of producing the desired L2header. The sequence can be of the form of a data structure thatincludes references to common components of L2 headers which can, bestored on-chip in an on-chip template as well as references to specificL2 header templates which are unique to a given next hop index. Theunique templates can be stored/off-chip in SRAM. Ethernet, Frame Relay,and other L2 header types are created and stored in templates.

The L2 header data structure includes three parts: a program header, L2header byte generation template and one or more templates. The programheader includes flags for initiating error checking functions and isused to define the size of the sequence. Error checking functionsinclude calculating a checksum for the L2 header.

The L2 byte generation template stores flags indicating which bytes ofthe data structure are generated from internal or external templates.

A template includes instructions for generating particular L2 headerdata for a given next hop index. In addition to generating a new L2header based on the next hop index, output formatter 314 can be requiredto manipulate portions of the L3 header that have been stored along withthe packet in packet memory (memory 104 in FIG. 2 b). For example,output formatter 314 calculates new checksum data for the L3 headerprior to transmission from the router.

Output formatter 314 couples the cell data returned from memory with,the appropriate media header (L2 header) to generate a complete packetfor transfer out of router 20 on the line output interface 308.

In-Line Packet Processing Overview

Referring now to FIG. 7, in a method for in-line processing packets forrouting through a switch, a packet is received at a multi-functionmultiport (702). Packet headers are pre-processed to the evaluate L2header data for errors and locate the start of the next layer header(704). L2 header data is conditionally stripped as part of thepre-processing (706). L3 header data is evaluated in parallel for errors(708). The cells are transferred to an input switch (710). Input switchremoves the key information from the first cell in a packet and routesthe cells to memory banks resident in the multi-function multiports in atime division multiplexed manner (712). The key, full address of thefirst cell and offset information is transferred as a look-up request toa controller (714). The controller performs a best match look-up andgenerates a result of the look-up (716). The result includes thedestination port (multi-function multipart), address, offset informationand next hop index. A notification including the result is transferredto the output switch for transfer to the appropriate multi-functionmultiport (718).

Upon receipt of a notification, the multi-function multiport generatesread requests a cell at a time to the input switch for the dataassociated with the packet (720). When the memory bank receives therequest from the input switch, cell data are transferred to anappropriate multi-function multipart through the output switch (722).Upon receipt, the multi-function multiport constructs a L2 header fromtemplates indicated by the next hop index and modifies the L3 header asappropriate (724). Finally, the cell data and media header informationis streamed to the destination (726) and the process ends (728).

The present invention has been described in terms of specificembodiments, which are illustrative of the invention and not to beconstrued as limiting. Other embodiments are within the scope of thefollowing claims.

1. A method of in-line processing a data packet while routing the packetthrough a router in a system transmitting data packets between a sourceand a destination over a network including a router, the methodcomprising: receiving the data packet; pre-processing layer header datafor the data packet as the data packet is received and prior totransferring any portion of the data packet to packet memory; storingthe data packet in the packet memory; determining a routing through therouter including a next hop index describing the next connection in thenetwork; retrieving the data packet from the packet memory; constructinga new layer header for the data packet from the next hop index while thedata packet is being retrieved from memory; and coupling the new layerheader to the data packet prior to transfer from the router. 2-38.(canceled)